Thermal transfer receiving sheet

ABSTRACT

There is provided a thermal transfer receiving sheet comprising a substrate, a barrier layer laminated on said substrate, and an image receiving layer laminated on said barrier layer, wherein said barrier layer and said image receiving layer are laminated on at least one side of said substrate, characterized in that the major components of said barrier layer are a swellable lamellar inorganic component and an adhesive, wherein said swellable lamellar inorganic component has a mean particle diameter of at least 0.1 μm and not greater than 100 μm, and an aspect ratio (ratio of mean particle diameter to thickness of the lamellar composite) of at least 100 and not greater than 5000.

FIELD OF THE INVENTION

The present invention relates to a thermal transfer receiving sheet.More specifically, it relates to a thermal transfer receiving sheet(hereinafter also referred to simply as “receiving sheet”) which has ahigh image quality and a high image stability, as well as an excellentanti-curl property during printing, and which is also inexpensive.

BACKGROUND ART

In recent years, there has been an increased interest in thermalprinters and, especially, in dye thermal transfer printers which allowprinting of clear full-color images. A dye thermal transfer printerforms an image by placing a dye-containing layer of the ink sheet ontoan image-receiving layer (hereinafter also referred to simply as“receiving layer”) comprising a dye-fixable resin on the receivingsheet, and then supplying heat from a thermal head or the like so as totransfer the dye at a predetermined location of the dye layer of the inksheet to the receiving layer. The ink sheets comprise dye layers ofthree colors: yellow, magenta and cyan, or four colors, if black is alsoincluded. A full-color image is obtained by repeatedly transferring thedye of each of the colors in sequence to the receiving sheet. Becausedye thermal transfer systems allow high-quality image recording, and arealso suitable for digital printing from recently popular digitalcameras, such systems are gradually replacing silver salt photography.

The receiving sheet is associated with a drawback of a poor imagestability, because the dyes transferred to the receiving layer penetrateinto the underlying layer over time, and are then diffused into thesubstrate (hereinafter also referred to as “bleeding”), whereby theimage would lose clarity.

This drawback becomes particularly pronounced when it is attempted toimprove the recorded image density or quality by forming an intermediatelayer comprising hollow or foam particles on a base sheet so as toimpart a cushioning property to the receiving sheet (for example,Japanese Unexamined Patent Publication (Kokai) No. 1-27996, JapaneseUnexamined Patent Publication (Kokai) No. 63-87286).

The thermal insulation property, smoothness and cushioning property areessential features for efficient utilization of heat from the thermalhead for printing, and they significantly affect the printed imagequality and image density. More specifically, in the course of printingan image, the receiving sheet contacts with the thermal head via the inksheet and is pressed from the opposite side by a rubber roll which isreferred to as a “platen roll”. Under the pressure applied from therubber roll, a receiving sheet with a good cushioning property willadhere completely to the ink sheet, with an absence of gaps, and allowuniform transfer of the ink for satisfactory image quality, but areceiving sheet with a poor cushioning property will adhere to the inksheet with gaps between it and the contacting ink sheet, whereby the inkwill be poorly transferred, due to the existence of gaps, resulting in anon-uniform image. Thus, the cushion property is one of the mostimportant qualities of a receiving sheet. Japanese Unexamined PatentPublication (Kokai) No. 9-99651 discloses the preferred sizes for hollowparticles in the intermediate layer (foam layer), for the purpose ofachieving an enhanced printing quality.

A receiving sheet fabricated by providing an intermediate layercontaining hollow or foam particles has a drawback of a significantlypoor image stability, because the dyes transferred to the receivinglayer penetrate into the underlying layer over time and, then, tend tobe diffused into the substrate (bleeding), whereby the image would loseclarity. Thus, a layer with high barrier properties (a barrier layer) isessential in order to prevent bleeding particularly in receiving sheetshaving an intermediate layer comprising hollow or foam particles.

Japanese Unexamined Patent Publication (Kokai) No. 6-227159 proposes amethod wherein a layer containing a lamellar inorganic pigment with anaspect ratio of 5-90 is provided on a hollow particle containing primercoating layer (intermediate layer), for the purpose of preventingpenetration of the receiving layer coating components or the solventused in the receiving layer coating composition. However, a layercontaining such a lamellar inorganic pigment having an aspect ratio inthe aforementioned range is not sufficient to prevent penetration of theimage-forming dye into the intermediate layer or substrate, and thusexhibits virtually no bleed-preventing effects. One of the reasons forthis is presumably that, unlike the penetration of the receiving layercoating components or the solvent used in the receiving layer coatingcomposition, with respect to a dye used in sublimation thermal transfer,penetration of the dye occurs at a molecular level. Bleeding may beprevented by increasing the coverage of the barrier layer. However,excessive increase of the coverage of the barrier layer will reduce thethermal insulating effect of the intermediate layer, whereby reduces theprinting density, and thus, results in unclear images. With ongoingsubstitution for silver salt photography in recent years, a demandexists for receiving sheets with higher image quality and a superiorimage stability, goals which require better techniques.

DISCLOSURE OF THE INVENTION

The present invention has been accomplished in light of theaforementioned circumstances, and its object is to provide a thermaltransfer receiving sheet which has high image quality and high imagestability, without bleeding of the printed images over time, and whichis also inexpensive while exhibiting an excellent anti-curl propertyduring printing.

As a result of much diligent research into the problems described above,the present inventors have solved all of the problems mentioned above byproviding a thermal transfer receiving sheet comprising a substrate, abarrier layer laminated on said substrate, and an image receiving layerlaminated on said barrier layer, wherein said barrier layer and saidimage receiving layer are laminated on at least one side of saidsubstrate, characterized in that the major components of said barrierlayer are a swellable lamellar inorganic component and an adhesive,wherein said swellable lamellar inorganic component has a mean particlediameter of at least 0.1 μm and not greater than 100 μm, and an aspectratio (ratio of mean particle diameter/thickness of the lamellarcomposite) of at least 100 and not greater than 5000.

According to a preferred embodiment, the thermal transfer receivingsheet further comprises a hollow particle-containing intermediate layerlaminated between the barrier layer and the substrate. The mean particlesize of the hollow particles is preferably at least 0.1 μm and notgreater than 20 μm and, in the barrier layer, an aqueous polymercompound is preferably used as the adhesive, while the aqueous polymercompound is preferably at least one selected from the group consistingof polyvinyl alcohol, ethylene-vinyl alcohol copolymer resins andethylene-acrylic acid copolymer resins.

The thermal transfer receiving sheet may also have an adhesive layer onthe side of the substrate opposite the image receiving layer side, andmay also have a release sheet having a release coating containing arelease agent on said adhesive layer, wherein said release sheet islaminated on the adhesive layer by its release coating side.

The receiving sheet of the present invention is an ultrahigh-qualityreceiving sheet which produces high quality images, has high imagestability without bleeding of printed images over time, and isinexpensive while exhibiting an excellent anti-curl property duringprinting. Thus, the present receiving sheet is highly valuable.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in greater detail.

The present inventors explored various barrier layer materials with theaim of overcoming the aforementioned problem of bleeding of thermaltransfer dye images. Polyvinyl alcohol and acrylic copolymer resins canform films on intermediate layers, but when a printing sheet having sucha film formed thereon is placed in a wallet or in a clothing pocket forlong periods, or when it is wetted by outdoor rain, the image suffers anotable degree of bleeding. That is, the resin mentioned above does notexhibit an adequate barrier property under highly humid conditions orwhen being directly exposed to water, and therefore cannot preventbleeding. Highly-crosslinked urethane resins are also known whichgenerally have a high barrier property, but when it is attempted toapply these as a barrier layer of the present invention, film formationon the intermediate layer will become difficult and, thus, an adequatebarrier property cannot be exhibited. While film formation can beachieved by a considerable increase of the coverage, and bleeding ofimages can thus be reduced, the hardness of urethane resins also reducesthe cushioning property and impairs the image quality and, in severecases, leads to cracking of the layer and a notably poor outerappearance. Urethane resins are also expensive, and thereforedisadvantageous in economic terms. The inventors therefore searched fora method which solves the problem of bleeding by means of a lamellarpigment. As a result of much diligent research, it was discovered that aremarkable bleeding prevention effect is exhibited by adding a swellablelamellar inorganic component to the barrier layer. This is due to theexceedingly high crystallinity of the swellable lamellar inorganiccomponent which does not permit passage of the thermal transfer dye.Accordingly, by laying the swellable lamellar inorganic components inparallel on the intermediate layer to form multiple laminated layers,while at the same time, by adhering the swellable lamellar inorganiccomponents to each other and also to the intermediate layer by means ofa polymer compound, a notable bleed-preventing effect was obtained.

As specific examples of swellable lamellar inorganic components, theremay be mentioned graphite, phosphate-based derivative-type compounds(such as zirconium phosphate-based compounds), chalcogen compounds,hydrotalcite compounds, lithium-aluminum complex hydroxides, clay-basedminerals (for example, synthetic mica and synthetic smectite), and thelike.

Graphite, phosphate-based inductor-type compounds (such as zirconiumphosphate-based compounds), chalcogen compounds, hydrotalcite compoundsand lithium-aluminum complex hydroxides are compounds or substances withlamellar structures formed by unit crystal layers stacked on each other,where a lamellar structure is defined as a structure wherein planes,each having atoms strongly bonded with each other by covalent bonds anddensely arranged therein, are stacked roughly in parallel by weakbonding forces such as Van der Waals forces.

A “chalcogen compound” is a dichalcogen compound of a Group IV (Ti, Zr,Hf), Group V (V, Nb, Ta) and/or Group VI (Mo, W) element, and it isrepresented by the formula MX₂ (wherein M is the aforementioned elementand X is a chalcogen (S, Se, Te)).

Clay-based minerals are generally categorized into a type with a bilayerstructure having an octahedral layer comprising aluminum, magnesium orthe like as the central metal on a tetrahedral layer of silica, and atype with a trilayer structure wherein a tetrahedral layer of silica issandwiched between two octahedral layers comprising magnesium or thelike as the central metal. As the former bilayer structure type, theremay be mentioned kaolinite and antigorite, and as the latter trilayerstructure type, depending on the number of interlayer cations, there maybe mentioned smectite, vermiculite and mica.

As specific clay-based minerals there may be mentioned kaolinite,dickite, nacrite, halloysite, antigorite, chrysotile, pyroferrite,montmorillonite, hectorite, tetrasilicic mica, sodium taeniolite,margarite, talc, vermiculite, xanthophyllite, chlorite and the like.Other examples may be found in the publication, “Nendo Kobutsugaku”[Clay Mineralogy] by Haruo Shiromizu, 1988, Asakura Shoten.

Preferably used among clay-based minerals as swellable lamellarinorganic components of the present invention are minerals of thesmectite, vermiculite and mica families. More preferred from among thesmectite family are, for example, montmorillonite, beidellite,nontronite, saponite, iron saponite, hectorite, sauconite, stevensiteand the like.

Instead of naturally-occurring materials (clay-based minerals), theseswellable lamellar inorganic components may also be synthetic forms orprocessed forms (for example, surface-treated with a silane couplingagent), and for example, there may be mentioned synthetic smectiterepresented by the formulaNa_(0.1-1.0)Mg_(2.4-2.9)Li_(0.0-0.6)Si_(3.5-4.0)O_(9.0-10.6)(OH and/orF)_(1.5-2.5). The method of producing synthetic smectite or syntheticmica may be any of three methods: hydrothermal reaction (see JapaneseUnexamined Patent Publication (Kokai) No. 6-345419), solid-phasereaction method or a molten method (see Japanese Unexamined PatentPublication (Kokai) No. 5-270815).

Hydrothermal reaction is a synthesis process comprising reacting anaqueous solution or aqueous slurry containing various raw materials suchas silicates, magnesium salts, alkali metal ions, alkali metal salts andfluoride ion in an autoclave or pipe reactor at a high temperature of100-400° C. under high pressure. Because crystal growth is slow in ahydrothermal reaction, it is generally impossible to obtain largeparticles, and virtually all of the particles have sizes between 10 and100 nm. Yet, it is still possible to produce large particles of 1 μm orgreater by hydrothermal reaction if the synthesis is carried out with alow concentration, low temperature and prolonged time. However, theexcessively high production cost in this case is a major problem.

Solid-phase reaction is a method in which synthetic mica is produced byreacting talc, an alkali silicofluoride and other raw materials forseveral hours in a temperature range of 400-1000° C. As a solid-phasereaction produces mica by causing elemental migration while leaving theoriginal talc structure (topotaxy), the quality of the resultingsynthetic mica depends on physical properties and impurities of theoriginal talc, and because elemental migration cannot be completelycontrolled, the purity and crystallinity of the synthetic mica is oftenlow.

A molten method is a method of producing synthetic mica or syntheticsmectite by melting an anhydrous silicate, magnesium oxide, aluminumoxide, potassium silicofluoride, potassium carbonate or another rawmaterial at the melting point of mica (for example, 1500° C.) or higher,and then slowly cooling to crystallization. Depending on the selectedheating step, this method may be accomplished by an external heat moltenprocess or an internal heat molten process. An external heat moltenprocess is a production method in which a crucible containing the rawmaterials is placed in a chamber at a temperature above the meltingpoint and heated, and is then transferred to a chamber at a temperaturebelow the melting point, but this process is costly due to the expenseof the crucibles. An internal heat molten process accomplishes heatedmelting of the raw materials by electrification in a vessel providedwith graphite (carbon) electrodes or metal electrodes, followed bycooling, and internal heat molten processes are usually employed formolten synthesis. Molten synthesis methods can produce syntheticproducts with controlled particle sizes by pulverization and sizesieving of the cooled and crystallized mass. As molten synthesis methodscan employ raw materials of high purity and allow uniform mixture of theraw materials by the melting step, they are advantageous from thestandpoint of allowing production of synthetic mica or syntheticsmectite with a high degree of crystallinity, large particle sizes andhigh purity.

As examples of synthetic swellable lamellar inorganic components, theremay be mentioned synthetic micas such as fluorophlogopite(KMg₃AlSi₃O₁₀F, molten or solid-phase reaction method), potassiumtetrasilicone mica (KMg_(2. 5)Si₄O₁₀F₂, molten method), sodiumtetrasilicone mica (NaMg_(2.5)Si₄O₁₀F₂, molten method), sodiumtaeniolite (NaMg₂LiSi₄O₁₀F₂, molten method) and lithium taeniolite(LiMg₂LiSi₄O₁₀F₂, molten method), or synthetic smectites such as sodiumhectorite (Na_(0.33)Mg_(2.67)Li_(0.33)Si_(4.0)O₁₀(OH or F)₂,hydrothermal reaction or molten method), lithium hectorite(Na_(0.33)Mg_(2.67)Li_(0.33)Si_(4.0)O₁₀ (OH or F)₂, hydrothermalreaction or molten method) and saponite(Nao_(0.33)Mg_(2.67)AlSi_(4.0)O₁₀(OH)₂, hydrothermal reaction method)Among these swellable lamellar inorganic components, there arepreferably used synthetic micas such as sodium tetrasilicone mica,sodium taeniolite and lithium taeniolite, synthetic smectites such assodium hectorite, lithium hectorite and saponite, and natural smectitessuch as montmorillonite. Sodium tetrasilicone mica is particularlypreferred among these, and the desired particle sizes, aspect ratios andcrystallinity can be obtained by molten synthesis.

As examples of commercially available clay minerals there may bementioned natural bentonite, commonly known as sodium bentonite, Kunipia(trade name of Kunimine Industries Co., Ltd., natural montmorillonite),Smectone (trade name of Kunimine Industries Co., Ltd., hydrothermalsynthesized smectite), Veegum (trade name of Vanderbilt, Inc.), Laponite(trade name of Laporte Industries Co., Ltd.), DM Clean A, DMA-350, Na-Ts(trade names of Topy Industries Co., Ltd., all three molten synthesizedmica, sodium tetrasilicone mica) and Bengel (trade name of Hojun Corp.),any of which may be used alone or in mixtures of two or more.

A swellable lamellar inorganic component preferably used for the presentinvention is a swellable lamellar inorganic component which readilyswells, cleaves and disperses in water. The degree of “swelling andcleavage” of the swellable lamellar inorganic component in the solventmay be evaluated by “swelling/cleavage” property tests. The swelling ofthe swellable lamellar inorganic component is preferably about 5 ml/2 gor greater, and more preferably about 20 ml/2 g or greater.

Specifically, the swelling forces of the swellable lamellar inorganiccomponents are, for example, as follows: Kunipia (swelling force: 65ml/2 g or greater), Smectone (swelling force: 60 ml/2 g or greater), DMClean A, DMA-350, Na-Ts (swelling force: 30 ml/2 g or greater), ME-100(trade name of Co-Op Chemical Co., Ltd., swelling force: 20 ml/2g orgreater) and Bengel (swelling force: 38 ml/2 g or greater).

The swelling property test will now be explained. Using a 100 mlgraduated cylinder as the test vessel, 2 g of the swellable lamellarinorganic component is slowly added to 100 ml of solvent and the mixtureis allowed to stand, and after 24 hours at 23° C., the volume of theswellable lamellar inorganic component dispersion layer is determined byreading the scale where the interface of the obtained swellable lamellarinorganic component dispersion layer and the supernatant layer exits. Alarger numerical value (ml/2 g) is preferred, indicating a higherswelling property. The solvent used is preferably water.

The cleavage property of the swellable lamellar inorganic component ispreferably at least about 5 ml, and more preferably at least about 20ml. The solvent used for measurement of the cleavage is a solvent havinga density lower than the density of the swellable lamellar inorganiccomponent, and it is preferably water.

The cleavage property test will now be explained. After slowly adding 30g of the swellable lamellar inorganic component to 1500 ml of theswelling solvent, the mixture is dispersed for 90 minutes using adisperser (trade name: DISPER MH-L, product of Asada Iron Works Co.,Ltd., 52 mm blade diameter, 3100 rpm, 3 L vessel volume, 28 mmbottom-blade distance) at a circumferential speed of 8.5 m/sec (solventtemperature: 23° C.), and then 100 ml of the dispersion is transferredinto a graduated cylinder and allowed to stand for 60 minutes, afterwhich the volume of the swellable lamellar inorganic componentdispersion layer is determined by reading the scale where the interfaceof the swellable lamellar inorganic component dispersion layer and thesupernatant layer exists.

The swellable lamellar inorganic component used has an aspect ratio of100-5000, and preferably an aspect ratio of 500-5000. An aspect ratio ofless than 100 may result in bleeding of images, while an aspect ratio ofgreater than 5000 may impair the image uniformity. The aspect ratio (Z)is represented by the relationship Z =L/a, where L is the mean particlediameter of the swellable lamellar inorganic component in water (asmeasured by laser diffraction, using an LA-910 by Horiba Co., Ltd.;median diameter at a volume distribution of 50%), and a is the thicknessof the swellable lamellar inorganic component. The thickness is thevalue determined by observation of a scanning electron microscopy (SEM)or a transmission electron microscopy (TEM) photograph of thecross-section of the barrier layer. The mean particle diameter of theswellable lamellar inorganic component is 0.1-100 μm, preferably 0.3-50μm and more preferably 0.5-20 μm. If the mean particle diameter is lessthan 0.1 μm, the aspect ratio will be too small and it may be difficultto lay the compound in parallel on the intermediate layer, making itimpossible to fully prevent bleeding of images. If the mean particlediameter is larger than 100 μm, the swellable lamellar inorganiccomponent may protrude out from the barrier layer producingirregularities on the barrier layer surface, thus impairing thesmoothness of the receiving layer and deteriorating the image quality.

According to the present invention, the adhesive used for formation ofthe barrier layer is preferably an aqueous polymer compound such as awater-soluble polymer or a water-dispersible resin. For example, theremay be mentioned water-soluble polymers including starch, modifiedstarch, hydroxyethyl cellulose, methyl cellulose, carboxymethylcellulose, gelatin, casein, gum Arabic, polyvinyl alcohols such astotally saponified polyvinyl alcohol, partially saponified polyvinylalcohol, carboxy-modified polyvinyl alcohol and acetoacetyl-modifiedpolyvinyl alcohol, resins such as ethylene-vinyl alcohol copolymerresin, diisobutylene-maleic anhydride copolymer salts, styrene-maleicanhydride copolymer salts, styrene-acrylic acid copolymer salts andethylene-acrylic acid copolymer salts, urea resins, urethane resins,melamine resins and amide resins, and water-dispersible resins such asstyrene-butadiene-based copolymer latexes, acrylic acid esterresin-based latexes, methacrylic acid ester-based copolymer latexes,ethylene-vinyl acetate copolymer latexes, polyester-polyurethaneionomers and polyether-polyurethane ionomers. These aqueous polymercompounds may be used alone or in mixtures of two or more.

Water-soluble polymer compounds are preferably used among these aqueouspolymer compounds, and for example, polyvinyl alcohol, ethylene-vinylalcohol copolymer resin and ethylene-acrylic acid copolymer resin arepreferably used, for a notable effect of improving image bleeding. Also,an excellent effect from the standpoint of water resistance can beobtained by using ethylene-vinyl alcohol copolymer resins andethylene-acrylic acid copolymer resins. The coating solution preparedusing a water-soluble polymer compound preferably has a suitably lowviscosity, as distinct images can be obtained presumably due to uniformdispersion of the water swellable lamellar inorganic component. Forexample, in the case of a totally saponified polyvinyl alcohol, thepolymerization degree is preferably no greater than 2000 and morepreferably no greater than 300-1000.

According to the present invention, the mixing ratio of the swellablelamellar inorganic component and the adhesive as the constituentmaterials of the barrier layer is preferably 1-100 parts by weight, andmore preferably 5-50 parts by weight, of the swellable lamellarinorganic component to 100 parts by weight of the adhesive. The materialof the barrier layer may be any of various inorganic or organicpigments, waxes, metal soaps and the like and, if necessary, there mayalso be used various additives such as ultraviolet absorbers,fluorescent dyes, oil repellents, antifoaming agents, viscositymodifiers, crosslinking agents, curing agents and the like, in rangeswhich do not interfere with the desired effect.

The solid coverage of the barrier layer is preferably 0.1-10 g/m², andmore preferably 0.5-5 g/m². If the solid coverage is less than 0.1 g/m²,the barrier layer will not form a sufficient film, and the desiredeffect of preventing image bleeding will not be exhibited. The solidcoverage is preferably not greater than 10 g/m² because thebleed-preventing effect will be saturated, creating an economicallyundesirable situation.

The substrate used for the receiving sheet of the present invention is apaper composed mainly of cellulose pulp, or a synthetic resin film. Forexample, there may be appropriately used woodfree paper (acid paper,acid-free paper), wood-containing paper, coated paper, art paper,glassine paper or resin laminated paper, or oriented film composedmainly of polyolefins such as polyethylene or polypropylene, polyesterssuch as polyethylene terephthalate, polyamides, polyvinyl chloride,polystyrene or the like, single-layer oriented film or multilayerstructured film composed mainly of thermoplastic resins such aspolyolefins (synthetic sheets), and composite film obtained bylaminating these films together, or by laminating one of these films toanother type of film or to paper. While there are no particularrestrictions, paper substrates composed mainly of cellulose pulp providea cost advantage, and a superior effect of the present invention canalso be obtained. The sheet-like substrate used for the presentinvention preferably has a thickness of 20-300 μm.

According to the present invention, the hollow particles used in theoptional intermediate layer may be microcapsules comprising a lowboiling point hydrocarbon such as n-butane, i-butane, pentane,neopentane or the like as the nucleus and a homopolymer or a copolymerresin of, e.g., polyacrylonitrile or methyl methacrylate, as the shell.

According to the present invention, the mean particle size of the hollowparticles after formation of the intermediate layer is preferably 0.1-20μm and more preferably 0.5-20 μm. For example, the intermediate layermay be formed by preparing an intermediate layer coating comprisingpre-expanded particles, or by preparing an intermediate layer coatingcomprising unexpanded particles, coating the intermediate layer, andthen expanding the particles. If the mean particle size of the hollowparticles in the intermediate layer exceeds 20 μm, the smoothness willbe impaired and the quality may be poor. If it is less than 0.1 μm, itmay not be possible to achieve adequate heat insulation, less ink may betransferred from the ink sheet, and the image density may therefore bereduced. The volume void fraction (hereinafter also referred to simplyas the “void fraction”) of the hollow particles is preferably 30-95%,because if the void fraction is less than 30%, the heat insulation maybe insufficient and adequate density may not be achieved. If it isgreater than 95%, the shell thickness of the hollow particles will bereduced, tending to result in problems such as collapse of the hollowparticles and lower heat insulation. The particle sizes of the hollowparticles are measured by a laser diffraction method, in the same manneras that for the swellable lamellar inorganic component mentioned above.The void fraction of the hollow particles may be determined based on thevolume specific gravity of the aqueous dispersion of the hollowparticles, the solid concentration, and the true specific gravity of theresin composing the hollow particle shells.

According to the present invention, the adhesive used in the optionalintermediate layer is, similar to the barrier layer, preferably anaqueous polymer compound such as a water-soluble polymer orwater-dispersible resin. Polyvinyl alcohol is preferred amongwater-soluble polymer compounds, and ethylene-vinyl acetate copolymerlatexes and acrylic acid ester resin-based latexes are preferably usedamong water-dispersible resins. The aforementioned water-soluble polymercompounds may be used alone, or mixtures of two or more thereof may beused.

According to the present invention, the mixing ratio of the hollowparticles and the adhesive as the constituent materials of the optionalintermediate layer is preferably 10-300 parts by weight, and morepreferably 80-250 parts by weight, of the hollow particles to 100 partsby weight of the adhesive. At less than 10 parts by weight of hollowparticles to 100 parts by weight of the adhesive, sufficient heatinsulation may not be obtained and the printed image density may bereduced, impairing the image quality. At greater than 300 parts byweight of hollow particles to 100 parts by weight of the adhesive, thecoated film strength may be reduced, and peeling or cracking of thecoated film may occur. The material of the intermediate layer may be anyof various inorganic or organic pigments, waxes, metal soaps and thelike, and if necessary, there may also be used various additives such asultraviolet absorbers, fluorescent dyes, oil repellents, antifoamingagents, viscosity modifiers and the like, in ranges which do notinterfere with the desired effect.

The solid coverage of the intermediate layer is preferably 1-50 g/m²,and more preferably 5-20 g/m². If the solid coverage of the intermediatelayer is less than 1 g/m², sufficient heat insulating and cushionproperties will not be obtained and the density will be reduced, thusimpairing the image quality. The solid coverage is preferably notgreater than 50 g/m² because the effect on the heat insulating andcushion properties will be saturated, creating an economicallyundesirable situation.

According to the present invention, the receiving sheet has aconstruction comprising an optional intermediate layer, followed by abarrier layer and receiving layer, formed in that order on a substrate,and the receiving layer used may be a publicly known sublimation dyethermal transfer receiving layer. The resin forming the receiving layeris a resin which has a high affinity for the dye which migrates from theink sheet and also a good dye fixability. As such dye fixable resins,there may be used polyester resins, polycarbonate resins, vinyl chloridecopolymers, polyvinyl acetal resins, cellulose derivative resins such ascellulose acetate butyrate, and acrylate resins. In order to preventfusion of the receiving layer with the ink sheet by heating with thethermal head during printing, it is preferred to add at least one typeof crosslinking agent, lubricant and release agent to the resin. Ifnecessary, one or more fluorescent dyes, plasticizers, antioxidants,ultraviolet absorbers or pigments may be added to the resin. Suchadditives may be combined with the receiving layer-forming componentsprior to coating. They may alternatively be coated above and/or belowthe receiving layer as covering layers separate from the receivinglayer.

The solid coverage of the receiving layer is preferably about 1-15 g/m²and more preferably 3-10 g/m². If the coverage of the receiving layer isless than 1 g/m², it may not be possible to fully cover the substratesurface with the receiving layer, which may result in reduced imagequality or fusion problems in which the ink sheet and receiving layerstick together upon heating with the thermal head. On the other hand, acoverage exceeding 15 g/m² is not only uneconomical due to saturation ofthe effect, but the coated receiving layer may be poor in strength orthe receiving layer thickness will increase, thus preventing an adequateheat insulating effect for the substrate and possibly reducing theprinting density.

The method of forming the coated layers for the intermediate layer,barrier layer, receiving layer, etc. may involve application of eachprepared coating solution using any of various coating apparatuses suchas an air knife coater, varibar blade coater, pure blade coater, rodblade coater, short dwell coater, curtain coater, die coater, gravurecoater, roll coater, spray coater, dip coater, bar coater, comma coater,offset roll coater, reverse roll coater, lip coater, slide bead coateror the like. When drying is required, it may be carried out by aconventional method in combination with these coating apparatuses. Whenradiation curing is required, an irradiating apparatus such as anultraviolet irradiating or electron beam irradiating apparatus may beappropriately used to accomplish curing.

The receiving sheet of the present invention may, if necessary, have aprimer coating layer formed beforehand for the purpose of preventingpenetration of the intermediate layer coating composition into thesubstrate during formation of the intermediate layer. Also, for thepurpose of preventing electrification of the receiving sheet, rectifyingcurls in the receiving sheet and preventing multi-feeding of thereceiving sheet in the printer during printing, a backing layer may alsobe provided on the back side of the receiving sheet. A super-calendertreatment may, of course, also be carried out.

Formation of a backing layer can result in a smoother procedure ofsupplying the receiving sheet to the printer, transporting it throughthe printer and ejecting it from the printer. The backing layer ispreferably composed mainly of a backing layer-forming resin, ifnecessary, with one or more lubricants, release agents, antistaticagents, organic and/or inorganic pigments or the like. The solidcoverage of the backing layer is preferably in the range of 0.3-10 g/m²,and even more preferably in the range of 1-5 g/m².

The receiving sheet of the present invention may also have a structurewherein the barrier layer and receiving layer are laminated in thatorder on one side of the substrate, and then an adhesive layer (apressure sensitive adhesive layer), release layer and release sheet base(throughout the present specification, the release sheet base with therelease layer will also be referred to as “release sheet”) laminated inthat order on the other side of the substrate. This structureconstitutes a seal type or label type receiving sheet which allowsattachment and release between the adhesive layer and release layer.According to another embodiment, therefore, the present inventionprovides a seal type or label type (hereinafter both referred to as“seal type”) receiving sheet.

A seal type receiving sheet preferably has an overall thickness of100-300 μm. If the thickness is less than 100 μm, the mechanicalstrength and rigidity of the receiving sheet may be insufficient, and itmay not be possible to adequately prevent curls in the receiving sheetwhich are produced during printing. If the thickness is greater than 300μm, the number of receiving sheets held by the printer will be small anda receiving sheet tray with greater volume will be necessary to hold apredetermined number of sheets, thus making it difficult to produce acompact printer.

(Adhesive Layer)

In a seal type receiving sheet of the present invention, the adhesiveresin used for the adhesive layer may be a publicly known adhesive resinsuch as an acrylic-based, rubber-based or silicone-based resin.Acrylic-based resins are preferred among such adhesive resins. Asacrylic-based resins there are preferably used resins composed mainly of2-ethylhexyl acrylate, butyl acrylate or ethyl acrylate, obtained bycopolymerization of these with one or more other (meth)acrylic acidesters (non-functional, or (meth)acrylic acid esters having variousfunctional groups), or other copolymerizable monomers. If necessary,tackifiers such as rosins and the like, isocyanate-based and epoxy-basedcrosslinking agents, age resisters, stabilizers, softeners such as oils,fillers, pigments, coloring agents and the like may be added to theseadhesive resins. Also, combinations of two or more thereof may be usedas necessary.

The solid coverage of the adhesive layer is preferably 5-30 g/m², andmore preferably 7-25 g/m². The adhesive layer may be formed by using acoater selected from among bar coaters, gravure coaters, comma coaters,blade coaters, air knife coaters, die coaters, curtain coaters, lipcoaters and slide bead coaters, for application of the adhesive layercoating solution by an ordinary method followed by drying.

As to the order for forming the adhesive layer, first the adhesive layercoating solution may be applied onto the release surface of the releaselayer formed on the release sheet base and dried to form an adhesivelayer, and then the adhesive layer surface may be attached by laminationagainst the substrate side having the receiving layer on the surface, orthe adhesive layer coating solution may be coated onto the opposite sideof the substrate having the receiving layer and dried to form theadhesive layer, and then the adhesive layer side and the release surfaceof the release sheet may be attached by lamination against each other.

(Release Sheet Base)

The release sheet base used for a seal type receiving sheet of thepresent invention may be the same as that for the substrate of thereceiving sheet. Preferred is a laminated sheet having a thermoplasticresin layer of a polyolefin resin or the like formed on at least oneside, or a film composed mainly of a synthetic resin such as a polyester(for example, polyethylene terephthalate). The thickness of the releasesheet base is preferably in the range of 20-200 μm, and more preferably50-150 μm.

(Release Layer)

According to the present invention, the used release-treated releasesheet may be one having, for example, a release layer formed on arelease sheet base, and the release layer may include a publicly knownrelease agent. The release agent used is preferably an emulsion-type,solvent-type or solvent free-type silicone resin, fluorine resin or thelike. In this case, the release layer coating solution is applied anddried on the release sheet base to a solid coverage of the release layerof 0.1-3 g/m² and more preferably of 0.3-1.5 g/m², and then it is curedby heat curing, an electron beam, ultraviolet curing or the like to formthe release layer. The method of forming the release layer is notparticularly restricted and, for example, a coater such as a bar coater,direct gravure coater, offset gravure coater or air knife coater may beused, as appropriate, for coating and drying of the release layercoating solution onto the release sheet base.

For a seal type receiving sheet, a backing layer may also be formed onthe side of the release sheet base opposite the side on which therelease layer has been formed. The backing layer of the release sheetbase is formed in the same manner as the backing layer on the receivingsheet, and formation of a backing layer on the receiving sheet sectionmay be omitted.

EXAMPLES

The present invention will now be explained in greater detail throughexamples, although the present invention is, naturally, not limited tothese examples. The “parts” and “%” values in the examples all refer to“parts by weight” and “wt %”.

Example 1

(Formation of Intermediate Layer Coated Sheet)

An intermediate layer coating solution was prepared by mixing andstirring 70 parts of an aqueous dispersion (solid concentration: 30%) ofexpanded hollow particles comprising a thermoplastic resin composedmainly of vinylidene chloride and acrylonitrile (mean particle size: 5.4μm, void fraction: 60%), 15 parts of an aqueous solution (solidconcentration: 10%) of polyvinyl alcohol (trade name: PVA217, KurarayCo., Ltd.) and 15 parts of styrene-butadiene latex (trade name: L-1537,solid concentration: 50%, Asahi Kasei). This was then applied and driedon one side of an art paper sheet (trade name: OK Kinfuji-N, basisweight: 186 g/m², Oji Paper Co. Ltd.) as the substrate using a diecoater to a dry coverage of 20 g/m², to form an intermediate layercoated sheet.

(Formation of Barrier Layer Coated Sheet)

A barrier layer coating solution was prepared by mixing and stirring 100parts of an aqueous solution (solid concentration: 10%) of polyvinylalcohol (trade name: PVA105, polymerization degree: approximately 500,Kuraray Co., Ltd.) and 4 parts of styrene-butadiene latex (trade name:L-1537, solid concentration: 50%, Asahi Kasei) with 100 parts of anaqueous dispersion of the swellable lamellar inorganic component sodiumtetrasilicone mica (mean particle diameter: 6.3 μm, 5% aqueousdispersion). The barrier layer coating solution was then applied anddried on the intermediate layer of the aforementioned intermediate layercoated sheet using a Meyer bar coater to a dry coverage of 3 g/m², toform a barrier layer coated sheet. The aspect ratio of the swellablelamellar inorganic component was 2700, as calculated from the thicknessmeasured by cross-sectional observation of the barrier layer coatedsheet.

(Formation of Backing Layer Coated Sheet)

A backing layer coating solution was prepared by mixing and stirring 100parts of an aqueous solution (solid concentration: 10%) of polyvinylalcohol (trade name: PVA117, Kuraray Co., Ltd.) and 20 parts of zincstearate (trade name: Z-8-36, solid concentration: 30%, Chukyo YushiCo., Ltd.). The backing layer coating solution was then applied anddried on the back side of the barrier layer coated sheet using a Meyerbar coater to a dry coverage of 2 g/m², to form a backing layer coatedsheet.

(Formation of Receiving Sheet)

A receiving layer coating solution was prepared by dissolving 100 partsof a polyester resin (trade name: BYLON-200, Toyobo Co., Ltd.), 2 partsof silicone oil (trade name: KF393, Shinetsu Kagaku) and 6 parts of anisocyanate compound (trade name: Takenate D-110N, Takeda PharmaceuticalCo., Ltd.) in 200 parts of a toluene/methyl ethyl ketone=1/1 (weightratio) mixed solvent, and mixing and stirring the solution. Thereceiving layer coating solution was applied and dried on the barrierlayer of the backing layer coated sheet using a gravure coater to a drycoverage of 6 g/m², to obtain a receiving sheet.

Example 2

A receiving sheet was prepared in the same manner as Example 1, exceptthat, instead of the expanded hollow particles comprising athermoplastic resin composed mainly of vinylidene chloride andacrylonitrile (mean particle size: 5.4 μm) for formation of theintermediate layer coated sheet of Example 1, there was used an aqueousdispersion (solid concentration: 30%) of expanded hollow particlescomprising a thermoplastic resin composed mainly of vinylidene chlorideand acrylonitrile but having a different particle size (mean particlesize: 1.6 μm, void fraction: 50%).

Example 3

A receiving sheet was prepared in the same manner as Example 1, exceptthat, instead of the expanded hollow particles comprising athermoplastic resin composed mainly of vinylidene chloride andacrylonitrile (mean particle size: 5.4 pm) for formation of theintermediate layer coated sheet of Example 1, there was used an aqueousdispersion (solid concentration: 30%) of expanded hollow particlescomprising a thermoplastic resin composed mainly of vinylidene chlorideand acrylonitrile but having a different particle size (mean particlesize: 18.1 μm, void fraction: 65%).

Example 4

A receiving sheet was prepared in the same manner as Example 1, exceptthat, instead of an aqueous dispersion of the swellable lamellarinorganic component, sodium tetrasilicone mica (mean particle diameter:6.3 μm, 5% aqueous dispersion), for formation of the barrier layercoated sheet of Example 1, there was used an aqueous dispersion of theswellable lamellar inorganic component sodium tetrasilicone mica with adifferent mean particle diameter (mean particle diameter: 14.5 μm, 5%aqueous dispersion). The aspect ratio of the swellable lamellarinorganic component was 4800, as calculated from the thickness measuredby cross-sectional observation of the barrier layer coated sheet.

Example 5

A receiving sheet was prepared in the same manner as Example 1, exceptthat instead of an aqueous dispersion of the swellable lamellarinorganic component, sodium tetrasilicone mica (mean particle diameter:6.3 μm, 5% aqueous dispersion), for formation of the barrier layercoated sheet of Example 1, there was used an aqueous dispersion of theswellable lamellar inorganic component sodium tetrasilicone mica with adifferent mean particle diameter (mean particle diameter: 1.5 μm, 5%aqueous dispersion). The aspect ratio of the swellable lamellarinorganic component was 180, as calculated from the thickness measuredby cross-sectional observation of the barrier layer coated sheet.

Example 6

A receiving sheet was prepared in the same manner as Example 1, exceptthat a barrier layer coated sheet formed by the following method wasused as the barrier layer coated sheet formed in Example 1.

(Formation of Barrier Layer Coated Sheet)

A barrier layer coating solution was prepared by mixing and stirring 100parts of an aqueous solution (solid concentration: 10%) ofethylene-vinyl alcohol copolymer resin (trade name: Exceval 4105,Kuraray Co., Ltd.) with 100 parts of an aqueous dispersion of theswellable lamellar inorganic component sodium tetrasilicone mica (meanparticle diameter: 6.3 μm, 5% aqueous dispersion). The barrier layercoating solution was then applied and dried on the intermediate layer ofthe aforementioned intermediate layer coated sheet using a Meyer barcoater to a dry coverage of 3 g/m², to form a barrier layer coatedsheet. The aspect ratio of the swellable lamellar inorganic componentwas 2700, as calculated from the thickness measured by cross-sectionalobservation of the barrier layer coated sheet.

Example 7

A receiving sheet was prepared in the same manner as Example 1, exceptthat a barrier layer coated sheet formed by the following method wasused as the barrier layer coated sheet formed in Example 1.

(Formation of Barrier Layer Coated Sheet)

A barrier layer coating solution was prepared by mixing and stirring 50parts of an aqueous solution (solid concentration: 28%) ofethylene-acrylic acid copolymer resin (trade name: ET-1000, Chuo RikaKogyo Co., Ltd.) with 100 parts of an aqueous dispersion of theswellable lamellar inorganic component sodium tetrasilicone mica (meanparticle diameter: 6.3 μm, 5% aqueous dispersion). It was then appliedand dried on the intermediate layer of the aforementioned intermediatelayer coated sheet using a Meyer bar coater to a dry coverage of 3 g/m²,to form a barrier layer coated sheet. The aspect ratio of the swellablelamellar inorganic component was 2700, as calculated from the thicknessmeasured by cross-sectional observation of the barrier layer coatedsheet.

Comparative Example 1

A receiving sheet was prepared in the same manner as Example 1, exceptthat a barrier layer coated sheet formed by the following method wasused as the barrier layer coated sheet formed in Example 1.

(Formation of Barrier Layer Coated Sheet)

A barrier layer-coated sheet was formed by using an aqueous solution(solid concentration: 10%) of polyvinyl alcohol (PVA105, Kuraray Co.,Ltd.) as the barrier layer coating solution, and coating and drying iton the intermediate layer of the intermediate layer coated sheet using aMeyer bar coater to a dry coverage of 5 g/m².

Comparative Example 2

A receiving sheet was prepared in the same manner as Example 1, exceptthat instead of an aqueous dispersion of the swellable lamellarinorganic component sodium tetrasilicone mica (mean particle diameter:6.3 μm, 5% aqueous dispersion) for formation of the barrier layer coatedsheet of Example 1, there was used an aqueous dispersion of muscovite asa non-swelling clay mineral (mean particle diameter: 20 μm, 5% aqueousdispersion). The aspect ratio of the non-swelling clay mineral was 55,as calculated from the thickness measured by cross-sectional observationof the barrier layer coated sheet.

Comparative Example 3

A receiving sheet was prepared in the same manner as Example 1, exceptthat instead of an aqueous dispersion of the swellable lamellarinorganic component sodium tetrasilicone mica (mean particle diameter:6.3 μm, 5% aqueous dispersion) for formation of the barrier layer coatedsheet of Example 1, there was used an aqueous dispersion of theswellable lamellar inorganic component sodium tetrasilicone mica with adifferent mean particle diameter (mean particle diameter: 105 μm, 3%aqueous dispersion). The aspect ratio of the swellable lamellarinorganic component was 7600, as calculated from the thickness measuredby cross-sectional observation of the barrier layer coated sheet.

Example 8

(Formation of Receiving Sheet Section)

An intermediate layer coated sheet was fabricated in the same manner asExample 1, except that an art paper sheet (trade name: OK Kinfuji-N,basis weight: 104.7 g/m², Oji Paper Co. Ltd.) was used as the substrateinstead of the art paper sheet (trade name: OK Kinfuji-N, basis weight:186 g/m², Oji Paper Co. Ltd.) for formation of the intermediate layercoated sheet.

The rest of the procedure was carried out in the same manner as Example1 to form a barrier layer and a receiving layer, in that order, on theintermediate layer of the intermediate layer coated sheet, to obtain areceiving sheet section. However, formation of the backing layer wasomitted.

(Formation of Release Sheet Base)

Low-density polyethylene also comprising titanium dioxide (trade name:YUKALON LK50, Mitsubishi Chemical Co., Ltd.) was coated by meltextrusion onto both sides of woodfree paper with a thickness of 67 μm(trade name: OK Woodfree Paper, basis weight: 52.3 g/m², Oji Paper Co.Ltd.), to 20 μm on each side, to obtain a release sheet base.

(Formation of Release Layer Coated Sheet)

A silicone-based release agent (trade name: KS830, Shinetsu Kagaku) wasthen coated and dried on one side of the obtained release sheet baseusing a gravure coater to a dry coverage of 0.5 g/m², to form a releaselayer coated sheet.

(Formation of Backing Layer Coated Release Sheet)

A backing layer coating solution was prepared by mixing and stirring 100parts of an aqueous solution (solid concentration: 10%) of polyvinylalcohol (trade name: PVA117, Kuraray Co., Ltd.) and 20 parts of zincstearate (trade name: Z-8-36, solid concentration: 30%, Chukyo YushiCo., Ltd.). The backing layer coating solution was then applied anddried on the side of the release layer coated sheet without the releaselayer, using a Meyer bar coater to a dry coverage of 2 g/m², to form abacking layer coated sheet.

(Formation of Seal-Type Receiving Sheet)

An adhesive layer coating solution was prepared by mixing and stirring400 parts of an acrylic-based adhesive (trade name: PE115E, solidconcentration: 23%, Nihon Carbide) and 3 parts of a curing agent (tradename: CK101, solid concentration: 75%, Nihon Carbide). The adhesivelayer coating solution was then coated and dried on one side of thebacking layer coated release sheet using a gravure coater to a drycoverage of 15 g/m², to form an adhesive layer coated release sheet.

The adhesive layer side of the adhesive layer coated release sheet wasplaced over the substrate side of the receiving sheet section (the sideopposite the receiving layer) and adhesively laminated to form a sealtype receiving sheet.

Example 9

A seal-type receiving sheet was prepared in the same manner as Example8, except for using an aqueous dispersion (solid concentration: 30%) ofexpanded hollow particles comprising a thermoplastic resin composedmainly of vinylidene chloride and acrylonitrile (mean particle size: 1.6μm, void fraction: 50%), as used in Example 2, for formation of theintermediate layer coated sheet.

Example 10

A seal-type receiving sheet was prepared in the same manner as Example8, except for using an aqueous dispersion (solid concentration: 30%) ofexpanded hollow particles comprising a thermoplastic resin composedmainly of vinylidene chloride and acrylonitrile (mean particle size:18.1 μm, void fraction: 65%), as used in Example 3, for formation of theintermediate layer coated sheet.

Example 11

A seal type receiving sheet was prepared in the same manner as Example8, except for using an aqueous dispersion of the swellable lamellarinorganic component sodium tetrasilicone mica (mean particle diameter:14.5 μm, 5% aqueous dispersion), as in Example 4, for formation of thebarrier layer coated sheet.

Example 12

A seal type receiving sheet was prepared in the same manner as Example8, except for using an aqueous dispersion of the swellable lamellarinorganic component sodium tetrasilicone mica (mean particle diameter:1.5 μm, 5% aqueous dispersion), as in Example 5, for formation of thebarrier layer coated sheet.

Example 13

A seal type receiving sheet was prepared in the same manner as Example8, except that the barrier layer was formed, by the same method as inExample 6, for formation of the barrier layer coated sheet.

Example 14

A seal type receiving sheet was prepared in the same manner as Example8, except that the barrier layer was formed, by the same method as inExample 7, for formation of the barrier layer coated sheet.

Example 15

A seal type receiving sheet was prepared in the same manner as Example8, except for using an oriented porous polyester film with a thicknessof 100 μm and composed mainly of polyethylene terephthalate (trade name:W900E100, Mitsubishi Chemical Polyester Film Co.) as the release sheetbase, for formation of the release layer coated sheet.

Comparative Example 4

A seal type receiving sheet was prepared in the same manner as Example8, except that the barrier layer coated sheet was formed by the samemethod as in Comparative Example 1, for formation of the barrier layercoated sheet.

Comparative Example 5

A seal type receiving sheet was prepared in the same manner as Example8, except that an aqueous dispersion of muscovite (mean particlediameter: 20 μm, 5% aqueous dispersion) was used as a non-swelling claymineral in the same manner as in Comparative Example 2, for formation ofthe barrier layer coated sheet.

Comparative Example 6

A seal type receiving sheet was prepared in the same manner as Example8, except that an aqueous dispersion of the swellable lamellar inorganiccomponent sodium tetrasilicone mica (mean particle diameter: 105 μm, 3%aqueous dispersion) was used in the same manner as in ComparativeExample 3, for formation of the barrier layer coated sheet.

Evaluation

The receiving sheets prepared in the aforementioned examples andcomparative examples were evaluated by the methods described below, andthe results are shown in Table 1.

“Print Quality” (Print Density, Image Uniformity)

Using a commercially available thermal transfer video printer (tradename: UP-DR100, Sony Corp.), ink sheets each having an ink layercontaining one of three different sublimating dyes: yellow, magenta orcyan, together with a binder formed on a 6 μm-thick polyester film, werecontacted in sequence with a receiving sheet, and the heat wascontrolled in stages with a thermal head for thermal transfer of apredetermined image into the receiving sheet, to accomplish printing ofan image with simple halftones of each color and superimposed colors.The reflection density of the recorded images transferred onto thereceiving sheet was measured using a Macbeth reflection densitometer(trade name: RD-914, Kollmorgen Co.), for each applied energy. Table 1shows the printing density as the concentration of the high tone sectioncorresponding to the 15th step from the lowest applied energy.

The uniformity of the recorded images at the tone section correspondingto an optical density (black) of 0.3 was visually evaluated, based onthe presence or absence of uneven density and dropouts. The evaluationresults were indicated as “good”, “fair”, or “poor” where notabledefects such as uneven density and dropouts were observed.

“Post-Printing Curl”

The receiving sheets prepared in the examples and comparative examples,each in roll form with a width of 127 mm, were fed to a thermal transferprinter (trade name: UP-DR100, Sony) for printing of black images, andwere cut at a length of 179 mm and ejected. The curling of the printedreceiving sheets was measured as the post-printing curl. As the methodof measuring the post-printing curl, the printed receiving sheet wasplaced on a level surface for 5 minutes, in an environment of 23° C.,50% RH, either with the receiving layer side facing upward (top curl) orthe receiving layer side facing downward (back curl), and the maximumheight among the four corners of each receiving sheet and the maximumheight recorded as the post-printing curl. The degree of post-printingcurl was evaluated on the following scale. “good”: Post-printing backcurl in a range of 0-20 mm. “fair”: Post-printing back curl in a rangeof greater than 20 mm and up to 30 mm, or top curl in a range of greaterthan 0 mm and up to 10 mm. “poor”: Post-printing back curl of greaterthan 30 mm or top curl of greater than 10 mm.

“Post-Printing Stability” (Image Bleeding)

Using a commercially available thermal transfer video printer (tradename: UP-DR100, Sony Corp.), ink sheets each having an ink layercontaining one of three different sublimating dyes: yellow, magenta orcyan together with a binder formed on a 6 μm-thick polyester film, werecontacted in sequence with a receiving sheet, and the heat wascontrolled in stages with a thermal head to accomplish thermal transferof a predetermined image into the receiving sheet, and printing of blackand blue narrow line images. This was followed by a post-printingstability acceleration test, wherein the image-printed sheet was allowedto stand for 2 weeks in an environment of 50° C., 95% RH. The imagebleeding rate was calculated according to the following formula (1).$\begin{matrix}{{{Bleeding}\quad{rate}} = {\frac{( {{thickness}\quad{of}\quad{line}\quad{after}\quad{standing}} )}{( {{thickness}\quad{of}\quad{line}\quad{before}\quad{standing}} )} \times 100}} & (1)\end{matrix}$

A bleeding rate of less than 110% was evaluated as “good”, a bleedingrate of at least 110% and less than 130% was evaluated as “fair”, and ableeding rate of 130% or greater was evaluated as “poor”. TABLE 1 Printdensity Image Post-printing Image (black) uniformity curl bleedingExample 1 2.24 good good good Example 2 2.12 good good good Example 32.39 good good good Example 4 2.21 good good good Example 5 2.29 goodgood good Example 6 2.29 good good good Example 7 2.34 good good goodComp. Ex. 1 2.23 good poor (top) poor Comp. Ex. 2 1.98 fair fair (top)poor Comp. Ex. 3 1.88 poor good good Example 8 2.22 good good goodExample 9 2.11 good good good Example 10 2.37 good good good Example 112.22 good good good Example 12 2.29 good good good Example 13 2.28 goodgood good Example 14 2.33 good good good Example 15 2.25 good good goodComp. Ex. 4 2.24 good poor (top) poor Comp. Ex. 5 1.97 fair fair (top)poor Comp. Ex. 6 1.86 poor good good

INDUSTRIAL APPLICABILITY

The present invention provides a thermal transfer receiving sheet whichproduces high quality images, has a high image stability withoutbleeding of printed images over time, is inexpensive and exhibits anexcellent anti-curl property during printing.

1 A thermal transfer receiving sheet comprising a substrate, a barrierlayer laminated on said substrate, and an image receiving layerlaminated on said barrier layer, wherein said barrier layer and saidimage receiving layer are laminated on at least one side of saidsubstrate, characterized in that the major components of said barrierlayer are a swellable lamellar inorganic component and an adhesive,wherein said swellable lamellar inorganic component has a mean particlediameter of a least 0.1 μm and not greater than 100 μm, and an aspectratio (ration of mean particle diameter/thickness of the lamellarcomposite) of at least 100 and not greater than
 5000. 2 A thermaltransfer receiving sheet according to claim 1, wherein an intermediatelayer comprising hollow particles is further laminated between saidbarrier layer and said substrate. 3 A thermal transfer receiving sheetaccording to claim 2, wherein the mean particle size of said hollowparticles is at least 0.1 μm and not greater than 20 μm. 4 A thermaltransfer receiving sheet according to claim 3, wherein the adhesive usedin said barrier layer comprises an aqueous polymer compound as a majorcomponent. 5 A thermal transfer receiving sheet according to claim 4,wherein said aqueous polymer compound is al least one selected from thegroup consisting of polyvinyl alcohol, ethylene-vinyl alcohol copolymerresins and ethylene-acrylic acid copolymer resins. 6 A thermal transferreceiving sheet according to claim 5, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side. 7 A thermal transferreceiving sheet according to claim 1, wherein the adhesive used in saidbarrier layer comprises an aqueous polymer compound as a majorcomponent. 8 A thermal transfer receiving sheet according to claim 7,wherein said aqueous polymer compound is al least one selected from thegroup consisting of polyvinyl alcohol, ethylene-vinyl alcohol copolymerresins and ethylene-acrylic acid copolymer resins. 9 A thermal transferreceiving sheet according to claim 8, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side. 10 A thermal transferreceiving sheet according to claim 2, wherein the adhesive used in saidbarrier layer comprises an aqueous polymer compound as a majorcomponent. 11 A thermal transfer receiving sheet according to claim 10,wherein said aqueous polymer compound is al least one selected from thegroup consisting of polyvinyl alcohol, ethylene-vinyl alcohol copolymerresins and ethylene-acrylic acid copolymer resins. 12 A thermal transferreceiving sheet according to claim 11, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side. 13 A thermal transferreceiving sheet according to claim 1, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side. 14 A thermal transferreceiving sheet according to claim 2, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side. 15 A thermal transferreceiving sheet according to claim 3, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side. 16 A thermal transferreceiving sheet according to claim 4, wherein said substrate has anadhesive layer on the side opposite the image receiving layer side, andalso has a release sheet having a release coating containing a releaseagent on said adhesive layer, where said release sheet is laminated tothe adhesive layer on its release coating side.